(A) Ribbon presentation of the Methanocaldococcus jannaschii aTrm5–tRNACys(GCA)–AdoMet complex structure. The fragment of structure typical for the AdoMet-dependent methyltransferases superfamily (SCOP: SSF53335) is colored gray (the remaining portion of aTrm5 is colored cyan). tRNACys is colored light orange, and G37 is presented as a stick model. SAM are depicted as stick models and carbon atoms are yellow. The residues that are key for catalysis32 are indicated in green.